Definition & Overview

Sleep studies are painless, non-invasive tests that are used to measure how well a person sleeps, how the body copes with sleeping problems, and determine the causes of the problem, if there are any. They work by recording the condition of the body during the different stages of sleep and are commonly used in the diagnosis of sleep disorders and determining their severity. These tests play a major role in the treatment of sleep disorders, which, when left alone, may increase a person's risk of several major health problems, such as heart disease, stroke, and high blood pressure.

Who should undergo and expected results

A person should undergo a sleep study if he experiences the early signs of sleeping disorders, such as:

  • any disturbing changes in the sleep cycle
  • having problems sleeping soundly
  • excessive snoring
  • difficulty staying awake, which is characteristic of a sleep disorder called narcolepsy
  • bstructed breathing during sleep, which is a characteristic of sleep apnea
  • sleepwalking
  • night terrors
  • bed-wetting
  • insomnia
  • twitching of the feet, arms, or legs repeatedly during sleep, which is a characteristic of a disorder called periodic limb movement disorder

Sleep apnea, a common sleep disorder, is one of the top reasons why people undergo sleep studies. A serious disorder, it stops the person's breathing several times during the night and these episodes last longer than 10 seconds.

Insomnia is also a common sleep disorder that most often observed in people who are going through a lot of stress, physical discomfort, or experiencing depression.

The sleep study is designed to diagnose different types of sleeping disorders so the patient can seek the most appropriate form of treatment.

How the procedure works

To understand how sleep studies work, there must first be an understanding of the different stages of sleep. The body enters two different stages during sleep; the non-rapid eye movement (NREM) stage and the rapid eye movement (REM) stage. In normal cases, the body alternates between REM and NREM for about 4 to 5 times during one night's sleep. If this normal alternating cycle is disrupted, the body will not be able to get a sound and complete rest.

A sleep study tries to detect any changes in the cycle by recording and observing different body functions during sleep. The specific information collected differs based on each type of sleep test, which may be any one of the following:

  • Multiple sleep latency test or MSLT – This is a sleep test that determines whether or not the patient enters the very important REM sleep stage. It is also effective in measuring the amount of time it takes a person to fall asleep, which can give clues about the presence of sleep disorders namely narcolepsy and idiopathic hypersomnia, both of which cause tiredness during the day. This is, however, a daytime sleep study, and is usually performed in conjunction with a polysomnogram, which is a nighttime test.
  • Polysomnogram – A polysomnogram observes the body's functions while a person is sleeping. It records the movement of the eyes, levels of oxygen and carbon dioxide in the body, rate and rhythm of the heart and breathing, snoring (if any), movements of the body muscles, rise and fall of the chest and belly, and most importantly, brain activity. These are recorded by sensors connected to the nose, face, scalp, and fingers, and elastic belt sensors that are placed on the chest and belly. The sensors transmit the information collected to a nearby computer, which is then read by a sleep lab technician.
  • Maintenance of wakefulness test or MWT – This test focuses on a person's ability to stay awake at a time when he should normally be awake. The test is conducted by asking the patient to try and stay awake for as long as possible while he is sitting on a comfortable chair. The test typically involves 4 repetitions of 40-minute long trials with an interval of 2 hours in between. Every time the patient falls asleep, the sleep lab technician will wake him up after 90 seconds.
  • Actigraphy – This is a special test used mainly for diagnosing problems with the body clock (or circadian rhythm) or a specific type of disorder called the shift work sleep disorder that usually affects people who work at night and sleep during the daytime. This test is conducted by making the patient wear a wrist device that records whether he is asleep or awake, so the attending physician can learn the usual routine of sleep and wake during a person's day.

Since a person has to fall asleep during a sleep study, certain preparations need to be done prior to undergoing such a test. Most specialists require patients to keep a sleep journal for about 1 or 2 weeks prior to the scheduled test. At least three days before the test, patients are advised to refrain from taking naps and drinking caffeinated food and beverages. They are also advised to refrain from taking any drugs or medications.

To make it easier for the patient to fall asleep during the test, sleep studies are usually scheduled in the evening, during the usual time of sleeping. The patient is then advised to take a shower or bath to relax the body, but must refrain from putting on any makeup, spray, oil, gel, or polish on the face, hair, and fingers, which can interfere with the test equipment that will be used.

Possible risks and complications

Sleep studies are a safe and painless way to detect the presence of various sleep problems, and they come with very little risk of complications. In fact, the only possible side effect is some redness on the skin where the electrodes are glued.


  • Collop NA, Anderson WM, Boehlecke B, et al. Clinical guidelines for the use of unattended portable monitors in the diagnosis of obstructive sleep apnea in adult patients. Portable Monitoring Task Force of the American Academy of Sleep Medicine. J Clin Sleep Med. 2007;3:737-747.

  • Epstein LJ, Kristo D, Strollo PJ Jr. Adult Obstructive Sleep Apnea Task Force of the American Academy of Sleep Medicine. Clinical guideline for the evaluation, management, and long-term care of obstructive sleep apnea in adults. J Clin Sleep Med. 2009;5:263-276.

  • Qaseem A, Holty JE, Owens DK, Dallas P, Starkey M, Shekelle P; for the Clinical Guidelines Committee of the American College of Physicians. Management of Obstructive Sleep Apnea in Adults: A Clinical Practice Guideline From the American College of Physicians. Ann Intern Med. Sep. 24, 2013.

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